1. Field of the Invention
The present invention relates to a light emitting element having a structure in which a plurality of layers are interposed between a pair of electrodes. Moreover, the present invention relates to a light emitting device having the light emitting element.
2. Description of the Related Art
A light emitting device utilizing light emitted from an electroluminescence element (a light emitting element) has been attracting attention as a display device or a lighting device.
As a light emitting element used for a light emitting device, a light emitting element in which a layer containing a light emitting compound is interposed between a pair of electrodes, is well known.
In such a light emitting element, one of the pair of electrodes serves as an anode and the other electrode serves as a cathode. Holes injected from the anode and electrons injected from the cathode are recombined to form excited molecules, and the light emitting element emits light when the excited molecules return to a ground state.
Meanwhile, demands for reduction in power consumption of display devices to be incorporated in various kinds of information processing apparatuses which have been rapidly developed, have been increased. In order to reduce the power consumption, it has been attempted to reduce driving voltage of a light emitting element. From the viewpoint of product commercialization, it is also important to prolong lifetime of a light emitting element in addition to the reduction in driving voltage. Development of a light emitting element has been carried out to overcome the above problems.
For example, in Japanese Patent Application Laid-Open No. Hei 9-63771 (the patent document 1), the reduction in driving voltage of a light emitting element is achieved by using-metal oxide having a high work function such as molybdenum oxide, as an anode (see the patent document 1).
However, only the means disclosed in the patent document 1 is not sufficient to prolong lifetime of a light emitting element. Therefore, development of a technique for achieving longer lifetime of a light emitting element, has been required.
In addition, since a light emitting element is generally formed using a thin organic film, for example, with a thickness of about 0.1 μm, the light emitting element has a problem that an upper electrode and a lower electrode are easily short-circuited to each other. In particular, low yield due to dust generated in a process of manufacturing a light emitting element, becomes a problem.